//https://leetcode-cn.com/problems/middle-of-the-linked-list/
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode middleNode(ListNode head) {
        ListNode slow , fast;
        slow = fast = head;
        //注意，判断条件和找环的判断条件不同
        while (fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;

        }

        return slow;
    }
}
